Lua tuple by table and tail-call.

tuple.lua

function tuple(arg) -- arg is table. 
	local n_arg = #arg
	if n_arg == 0 then
		return nil;
	end

	if n_arg == 1 then
		return  arg[1];
	end

	local function getTupleValue(n, idx, t_arg)
			if n == idx then
				return t_arg[idx]
			end

			return t_arg[idx], getTupleValue(n, idx+1, t_arg)
	end

	return arg[1], getTupleValue(n_arg, 2, arg)
end